More and more manufacturers are using rapid prototyping techniques to facilitate bringing products to market with decreasing lead times and development costs. The term "rapid prototyping" conventionally defines automatic techniques for producing a solid three-dimensional object via a computer model. Specifically, a computer model is utilized to produce thin plane cross-sections of a part. These crosssections, or layers, are then used as the building blocks of the prototype part with each of the layers being cut or formed separately.
Rapid prototyping techniques typically start with a computer aided design (CAD) representation or model of a part. The CAD model is then "sliced" graphically into a series of parallel cross sections spaced at a distance equal to the eventual thickness of the physical layers used to make the prototype part. Each physical layer is registered with respect to previous layers, and layers are bonded together via process-specific mechanisms such as melting, gluing, and sintering. For example, U.S. Pat. No. 5,847,958 to Shaikh et al. describes a process for rapidly prototyping a contoured part wherein a three-dimensional CAD model of the part is created and then sectioned into a plurality of graphical slabs. Physical solid members are machined for each graphical slab and then are joined together to replicate the CAD model. U.S. Pat. No. 5,779,833 to Cawley et al. describes a process for creating ceramic parts from a plurality of contoured layers that are separately made and then secured to each other via a sintering process.
There are considerable benefits associated with rapid prototyping. These include: reducing the amount of time required for a product to reach the market; enhancing the ability to perform functional, form and fit testing of a part; and facilitating low cost, small volume production.
Despite these benefits, current rapid prototyping processes suffer from several drawbacks. First, rapid prototyping equipment is quite expensive, with costs typically ranging between $100,000 and $500,000. Another drawback associated with conventional rapid prototyping is the length of time typically required to produce a prototype part. Conventional rapid prototyping techniques can take up to twenty-four hours to produce a single prototype part once a computer model of the part has been created.
A third drawback associated with conventional rapid prototyping is the general inability to produce strong parts that can be used directly in products or assemblies. Most current rapid prototyping processes produce relatively low-strength parts, typically out of paper, wax, or other low-strength materials. Rapid prototyping processes that do utilize stronger materials such as plastics, ceramics, and metals, often suffer from material weakness due to porosity, brittleness, incomplete bonding of layers, and even degradation over time.
Yet another drawback associated with conventional rapid prototyping is the inability to produce parts having accurate and precise geometries. For example, curved surfaces often have a "stair-step" appearance when multiple layers are assembled together. In addition, parts having undercut regions can be difficult to produce via the assembly of multiple layers. This is because it may be difficult to support layers that overhang undercut regions during assembly of the layers.